The invention relates to a frame converting device having a function to continuously output a plurality of image signals in a synchronized state while switching the image signals from a plurality of asynchronous inputs, and a function to extract a desired one of the continuous image signals from such plural inputs and outputs the extracted signal, and particularly, to improvement of a monitoring function when reproducing a recorded signal.
A known image switcher switches image signals from a plurality of cameras and the like and outputs the signals as one image signal. In switching such image signals, the input image signals from the cameras are often asynchronous with each other, but the disturbance of synchronous signals in the output image signals is inconvenient. In such case, all the input image signals are synchronized in advance by using a camera having a TBC (Time Base Corrector) function. Otherwise, asynchronous-synchronous conversion must be performed for each input by using a frame-converting device having a frame memory.
First problem: a camera having the TBC function is expensive, and therefore it is difficult to use the camera in a low-price route. Further, in the frame-converting device, the number of frame memories is the same as that of input image signals. While an image signal is stored into one of the frame memories, reading from another frame memory is performed.
Second problem: this type of device selects a either one of a first operation to switch the image signals from the plurality of cameras to outputs them as one image signal and to perform monitor display or VCR recording, or a second operation to extract a desired image signal from image signals from the plurality of cameras, switched to form one signal, and reproduced on a VCR or the like, and to perform display based on the extracted signal on the monitor.
In such frame-converting device, the number of frame memories must be the same as that of input image signals. This increases the price of the device. Further, the monitor display, and the VCR recording operation and cannot be performed in parallel to the VCR reproduction operation.